The number of different proteins and protein isoforms in the human proteome is estimated to be about three orders of magnitude higher than the number of genes encoded in the genome. This diversity is largely due to post-translational modification of proteins, Such modifications can have a significant impact on protein function and stability.
The Ubiquitin-Like (Ubl) molecule family play a prominent role in post-transcriptional modification-based protein regulation. The Ubl molecule family are a class of evolutionarily conserved polypeptides that can be reversibly conjugated to lysine residues on the proteins they regulate through the formation of isopeptide bonds. The binding of a Ubl to a protein can affect the protein's activity, stability, cellular localization and/or its interaction with other proteins. Some Ubl conjugation pathways are known to be important in various human diseases, including in cancer, viral infection and neurodegenerative disorders. More than a dozen Ubl family members have been identified to date.
FAT10 is a Ubl that is homologous to di-ubiquitin and has been suggested to be the only Ubl modifier that targets proteins for degradation through conjugation. However, the only in vivo covalent substrates of FAT10 identified to date are Ube2z and p53. It is therefore unclear whether FAT10 acts as part of a signaling pathway or acts to funnel proteins to the proteasome for degradation. The role of FAT10 in human disease remains unknown.